ESR has given another interview in which he talks about what drives open source developers and how dispersed groups of developers can produce reliable code that works.

One of the most powerful features of the open-source model is its capacity to hold down global complexity. The structure of work and communication in the hacker community is decentralized and distributed. Also, many different groups of people are working on many different software modules, each of which is relatively small and simple, and all of which have to be compatible in the end. That's a good way to write software.